The present invention relates to an internal chill casting method for manufacturing a cast product containing a pipe, which serves as a hydraulic circuit, therein while holding the pipe at a predetermined position of a cavity during pouring a molten aluminum alloy.
A product containing an inner hydraulic circuit has been manufactured so far by drilling a cast body. However, formation of a complicated hydraulic circuit is impossible by drilling, and an opening formed by drilling must be plugged. On the other hand, formation of such a hydraulic circuit is easy according to an internal chill casting method, whereby a pipe (hereinafter referred to as xe2x80x9can insert memberxe2x80x9d) is located at a predetermined position in a cavity of a mold and a molten metal (hereinafter referred to as xe2x80x9can enclosing materialxe2x80x9d) is then poured to the cavity. The internal chill casting method also facilitates post-processing of a cast product.
A pipe to be enclosed in a cast product is coated with heat insulating material or plated with a proper metal layer, in order to inhibit melt-down and to improve its adhesiveness to the enclosing material. In some cases, the pipe is cooled by supply of a cooling medium therein during pouring a molten metal.
When a molten metal is poured into a cavity of a mold having a pipe arranged therein, the pipe (the insert member) is likely dislocated due to a pressure of the molten metal. If the pipe is fixed at a dislocated position in a cast body, a hydraulic circuit can not be formed with a predetermined pattern. Deviation of the hydraulic circuit from the predetermined pattern causes troubles in the following steps. For instance, when the pipe-enclosing cast product is used as a brake caliper having an inner hydraulic circuit, attachments such as a bleed screw can not be coupled with the hydraulic circuit with high reliability.
The inventors proposed a method of inhibiting dislocation of a pipe during casting, as disclosed in JP 2000-254768A. According to the proposed method, the pipe is fixed in a cavity of a mold by clamping both ends of the pipe between upper and lower mold members or fixed with a core. Such a pipe held in a mold is heated up to a high temperature with a heat from a molten aluminum alloy poured into the cavity, so as to be thermally expanded or deformed. If both ends of the pipe are clamped between the metal mold members under such conditions, a middle part of the pipe apart from the clamped ends is likely to change its position. In some cases, a gap between the pipe and an inner surface of the mold becomes narrower. The pipe may project to the outside from a cast product. If the pipe in the cast product is greatly deviated from a predetermined position, it is necessary to form a big hole for coupling a bleed screw or the like to the pipe.
The present invention aims at provision of a cast product containing an hydraulic circuit therein without problems as above-mentioned. Formation of such a hydraulic circuit with high accuracy corresponding to a predetermined pattern is realized by fixing a controlling member, which controls a deforming direction of a pipe caused by thermal expansion, to a mold so as to hold the pipe at a predetermined position in a cast body.
According to the present invention, a controlling member is fixed to a mold in such the manner that it extends toward a cavity of the mold. A pipe (an insert member) is held in the cavity by insertion of the controlling member into at least one opening of the pipe or by inserting at least one end of the pipe into a hole of the controlling member. Thereafter, a molten aluminum alloy is poured into the cavity so as to enclose the pipe in a cast body.
The controlling member is preferably one, which adjustably extends through a wall of the mold into the cavity. Such an adjustable controlling member facilitates positioning of the pipe and ejection of a cast product. When a pin is used as the controlling member, the pipe is held at a predetermined position by inserting a tip of the pin into an opening of the pipe. The pin may be stepped at a middle part toward its tip, or an inner surface of the pipe may be chamfered at the opening, in order to inhibit inflow of a molten alloy into the pipe.
The stepped pin can have a shaft of a diameter larger than an inner diameter of the pipe, so its heat capacity is big enough to rapidly solidify a molten alloy in contact with the stepped part. Consequently, the pipe is protected from inflow of the molten alloy. Such the step is favorably formed with a right angle at a middle part of the pin, so as to enable insertion of the pin in face-to-face contact with a surface of the pipe.
The chamfered inner surface of the pipe at the opening arises a surface tension effective for suppressing inflow of a molten alloy into the pipe. Inflow of a molten alloy is also inhibited by coating the pin with a single or complex layer of such elements or compounds as Ti, TiN, TiC, CrN and BN, which are poor of wettability to a molten aluminum alloy, or by chemical conversion of a surface of the pin to a nitrided state or the like.
A controlling block having a hole for insertion of an end part of the pipe therein may be used, instead of the pin having a tip inserted into the opening of the pipe. The pipe may be also held at a predetermined position in the cavity, by attaching a bracket to the pipe, fixing the bracket at a predetermined position of a mold facing to the cavity, and inserting a controlling pin through a wall of the mold into a hole of the bracket.
An end of a pipe, with which the controlling member is coupled, may be located at a position apart from an inner surface of the mold toward the cavity. A cast product obtained in this case contains the pipe having the end declined from its surface, so that a properly predetermined profile of the controlling member can be transferred to an inner part of the cast product. Consequently, a working hole for attachment of a bleed screw can be designed to a size smaller than a diameter of the pipe, in a process of manufacturing a brake caliper.
The declined end of the pipe also advantageously assures the state that a boundary between the pipe and the enclosing material is not exposed on a surface of the cast product, and improves quality of the cast product. For instance, the cast product is machined to a proper shape with ease, since the pipe and the enclosing material different in hardness from each other are not simultaneously machined.
A gas pressure may be applied to the pipe during pouring a molten aluminum alloy into the cavity of a mold. The gas pressure effectively inhibits inflow of the molten alloy into the pipe and also maintains an initial shape of the pipe. Cool gas such as inert gas may be supplied into the pipe for application of such a gas pressure. Melting of the pipe can be also inhibited by the cool gas.
One open end of the pipe fixed to the mold may be shut with a plug, so as to expand a gas in the pipe with a heat during pouring a molten aluminum alloy. Such thermal expansion of the gas keeps the interior of the pipe at a positive pressure effective for inhibiting inflow of the molten alloy.